Cambridge has experienced a sharp upturn in bank robberies during the past three months, with more heists occuring since January than in all of 1989, police officials said yesterday.

The trend continued yesterday when an unidentified man stole an undetermined amount of money from a Bank of Boston branch in Alewife, bringing the number of robberies in the city this year to 10--two more than were reported last year, police said.

The perpetrator, described as a white man wearing a red cap and a plaid shirt, entered the Alewife branch of the Bank of Boston at about 12:30 p.m., passed a note to a teller and left with a bag of cash, police said.

Banks are wary of the sharp increase in robberies and following security measures carefully, officials said yesterday.

"You hear about these instances and you try to prepare yourself," said Lisa Carbone, a senior vice president of BayBank Harvard Trust.

Just after noon on March 12, a man claiming to have a bomb robbed the BayBanks branch at 2525 Mass. Ave. in North Cambridge. But Carbone said that her bank had been "fortunate" enough to have only one robbery. She attributed the recent upswing to the area's faltering economy.

"One thing to do is to look at it in relation to economic conditions. When times get tougher, people get desparate," Carbone said.

Cambridge police Lt. Timothy Lane said that the city is simply seeing the effect of a regional jump in the number of bank robberies.

"We're not alone in this. Other communities are going through this, too," Lane said.

Asked if bank robberies were on the increase in the local area, an agent at the Federal Bureau of Investigation's Bank Robbery Task Force answered, "Are they ever."

The agent referred further questions to an FBI spokesperson, who did not return a telephone call from The Crimson yesterday.

Cambridge police said one suspect is wanted in connection with several of the robberies, but most of them are believed to be unrelated.

The only Harvard Square bank branch to have been a target in the recent rash of robberies was the Coolidge Bank on Mt. Auburn St., according to police reports.

A Coolidge Bank spokesperson said yesterday that bank policy barred her from talking about robberies or security measures.